PROJECT SUMMARY The neocortex, including primary visual areas, sends massive projections to the striatum where they are thought to influence activity in the basal ganglia and, ultimately, goal-directed behavior. Despite the link between basal ganglia dysfunction and neurological disorders such as Huntington?s and Parkinson?s disease, the organization and function of corticostriatal circuits is not well understood. For example, to what extent do sensory maps in the neocortex transfer to the striatum? How is activity between cortical areas that send converging inputs to striatal subregions coordinated during behavior? Addressing these questions requires innovative approaches to tracing neural circuits and monitoring neuronal activity across multiple spatial scales in behaving animals. Here, I take advantage of several novel methodologies developed by our labs to investigate visual corticostriatal function in sensory-guided behavior. In Aim 1, I will map the fine-scale organization of visual inputs to the dorsomedial striatum. I will then monitor the activity of corticostriatal neurons in vivo to determine what visual information they represent and how they coordinate with large-scale cortical networks, making use of dual 2-photon and wide-field mesoscopic calcium imaging. In Aim 2, I will investigate the activity of corticostriatal cells and their associated large-scale networks in a visual detection task, combining these studies with optogenetic manipulations to causally test the role of these circuits in sensory-guided behavior. My results will generate fundamental insights into the organization of corticostriatal circuits. Moreover, these studies will provide me with an outstanding training opportunity to broaden my conceptual and methodological skills, supporting my long-term goal to become an independent scientist.